1. Field of the Invention
The present invention relates to a PLC (planar light wave circuit) type optical waveguide device comprising a planar optical waveguide substrate and an optical waveguide formed on the optical waveguide substrate, and a method of manufacturing the optical waveguide device, and more particularly, to an optical waveguide device formed by coupling a plurality of PLC type optical waveguide chips, and a method of manufacturing such optical waveguide device.
2. Description of the Related Art
At first, an example of the PLC type optical waveguide device comprising a planar optical waveguide substrate and an optical waveguide formed on the optical waveguide substrate will be described with reference to FIG. 1.
FIG. 1 is a perspective view showing, in outline, the construction of a PLC type optical waveguide device disclosed in Japanese Patent Application No. 28278/2000 filed on Feb. 4, 2000 by the same assignee as that of the present application. The optical waveguide device 30 comprises: an optical waveguide substrate 31 of generally rectangular shape in plan and made of, for example, silicon (Si); a generally xe2x80x9cyxe2x80x9d-shaped optical waveguide 2 made of glass layer or organic material thin film and formed on the surface of the optical waveguide substrate 31; a clad layer 32 made of glass layer or organic material thin film and formed on the surface of the optical waveguide substrate 31 in such manner that the optical waveguide 2 is covered with the clad layer 32; and a light source 33 that is a laser diode in this example and a photodetector 34 that is a photodiode in this example mounted on the optical waveguide substrate 31 at the both sides thereof in the longitudinal direction thereof respectively. Further, in the figure, though the optical waveguide 2 is shown in the manner that the top surface thereof is exposed, in reality, the top surface of the optical waveguide 2 is also covered with the clad layer 32. In addition, a lower clad layer made of glass layer or organic material thin film has been formed under the optical waveguide 2. The optical waveguide 2 corresponds to the core of an optical fiber having high refractive index, and the lower clad layer and the clad layer 32 (upper clad layer) correspond to the clad of the optical fiber having low refractive index.
The xe2x80x9cyxe2x80x9d-shaped optical waveguide 2 is constituted by two optical waveguides, one of which is an optical waveguide that forms a generally straight line and extends from one end surface of the optical waveguide substrate 31 in the longitudinal direction thereof to the other end surface of the optical waveguide substrate 31 in the longitudinal direction thereof, the other end surface being opposed to the photodetector 34, and the other of which is an optical waveguide which is branched from the central portion of the aforesaid optical waveguide of generally straight line and extends to the end surface of the optical waveguide substrate 31 opposed to the light source 33. Herein, the optical waveguide branched from the central portion of the optical waveguide of generally straight line will be referred to as first optical waveguide 21, one portion of the optical waveguide of generally straight line extending from the intersection or junction with the first waveguide 21 to the aforesaid one end surface of the optical waveguide substrate 31 in the longitudinal direction thereof will be referred to as second waveguide 22, and the other portion of the optical waveguide of generally straight line extending from the intersection to the other end surface (opposed to the photodetector 34) of the optical waveguide substrate 31 in the longitudinal direction thereof will be referred to as third waveguide 23.
The light source 33 is mounted on the optical waveguide substrate 31 such that the light emitting portion thereof is opposed to one end (a portion exposed on the end surface of the clad layer 32) of the first optical waveguide 21. One end (a portion exposed on the end surface of the clad layer 32) of the second optical waveguide 22 is optically coupled to other optical waveguide (for example, an optical fiber) not shown. The photodetector 34 is mounted on the optical waveguide substrate 31 such that the light receiving portion thereof is opposed to one end (a portion exposed on the end surface of the clad layer 32) of the third optical waveguide 23.
Between the intersection of the first and second optical waveguides 21 and 22 and the other end of the third optical waveguide 23 is formed a slit or groove 35 across the optical waveguide substrate 31 at substantially a right angle thereto, the slit 35 extending from the surface of the clad layer 32 into the optical waveguide substrate 31. Accordingly, the intersection of the first and second optical waveguides 21 and 22 is disconnected and separated from the other end of the third optical waveguide 23 by the slit 35, and the intersection of the first and second optical waveguides 21 and 22 is opposed to the other end of the third optical waveguide 23 through the slit 35.
Further, in this example, the slit 35 was formed by dicing (diecutting), but it is needless to say that the slit 35 may be formed by other cutting process. In addition, the light source 33 and the photodetector 34 are mounted directly on the optical waveguide substrate 31. A sheet of glass or a thin film of organic material is used as the clad layer 32, the thickness of the clad layer 32 being set to a value between several micrometers and about 20 micrometers in view of its strength.
A dielectric multilayer film filter 36 is inserted into the slit 35 and is fixed to the clad layer 32 by use of an appropriate adhesive 37. As a result, the end surface of the third optical waveguide 23 is opposed to the end surface of the intersection of the first and second optical waveguides 21 and 22 through the dielectric multilayer film filter 36. Further, a process of making the optical waveguide 2 is described in detail in Japanese Patent Application No. 28278/2000 mentioned above, and the explanation thereof will be omitted here.
The optical waveguide device 30 constructed as described above operates as a WDM (wavelength division multiplexing) device. For example, when light L1 having its wavelength of 1.31 xcexcm emitted from the light source 33 is incident on the end surface of the first optical waveguide 21, this light L1 propagates through the first optical waveguide 21 and is incident on the dielectric multilayer film filter 36. Since the characteristic of the dielectric multilayer film filter 36 is previously set such that it reflects light having its wavelength of 1.31 xcexcm, the dielectric multilayer film filter 36 reflects the light L1 incident thereon and inputs the light L1 into the end surface of the second optical waveguide 22. Accordingly, the light L1 propagates through the second optical waveguide 22 and is emitted to the outside (or to other optical waveguide not shown) from the other end surface of the second optical waveguide 22. On the other hand, when light L2 having its wavelength of 1.55 xcexcm is incident on the other end surface of the second optical waveguide 22 from the outside or other optical waveguide, this light L2 propagates through the second optical waveguide 22 and is incident on the dielectric multilayer film filter 36. Since the characteristic of the dielectric multilayer film filter 36 is previously set such that it transmits light having its wavelength of 1.55 xcexcm, the dielectric multilayer film filter 36 transmits the light L2 incident thereon and inputs the light L2 into the end surface of the third optical waveguide 23. Accordingly, the light L2 propagates through the third optical waveguide 23 to the other end surface thereof and is incident on the photodetector 34. Thus, the above-mentioned optical waveguide device 30 operates as a WDM device.
In the optical waveguide device 30, in case the dielectric multilayer film filter 36 is thick in its thickness, a loss of light transmitted through the filter 36 is increased. Therefore, for the purpose of making the optical characteristic of the dielectric multilayer film filter 36 good, the thickness of the dielectric multilayer film filter 36 is decreased as far as possible (usually, the dielectric multilayer film filter 36 is made to have its thickness of 10 xcexcm or so). However, it is impossible to make the loss of light transmitted through the filter 36 nothing (zero). In addition, the dielectric multilayer film filter 36 is inserted into the slit 35 for insertion of filter. In such case, it is required that the width of the slit 35 is broader by several xcexcm than the thickness of the dielectric multilayer film filter 36 because the dielectric multilayer film filter 36 cannot be inserted into the slit 35 in reality if the slit 35 should not be broader in its width than the thickness of the filter 36 by several xcexcm. Accordingly, the width of the slit 35 becomes considerably broader than the thickness of the filter 36 itself. As a result, in this respect, too, the loss of light is increased, and hence use of the dielectric multilayer film filter by inserting it into the slit has caused a disadvantage that the characteristic of the WDM device is deteriorated. Moreover, cutting process of the slit with high accuracy by dicing, and insertion and adhesion processes of the dielectric multilayer film filter need much time and prodigious labor as well as are lacking in mass production, which results in high manufacturing cost of the optical waveguide device.
In order to eliminate the disadvantages of the prior art described above, there is provided an optical waveguide device in which the optical waveguide device is cut at the position thereof into which a dielectric multilayer film filter is to be inserted, and the dielectric multilayer film filter is formed on an end surface of an optical waveguide by deposition of a dielectric multilayer film thereon. An example of the optical waveguide device of this type is shown in FIG. 2. Further, portions and elements in FIG. 2 corresponding to those in FIG. 1 will be denoted by the same reference characters affixed thereto, and the explanation thereof will be omitted unless it is necessary.
The optical waveguide device 40 shown in FIG. 2 is constituted by two optical waveguide chips 40A and 40B, and these two optical waveguide chips 40A and 40B are obtained, in this example, by cutting the optical waveguide device 30 shown in FIG. 1 in two exact halves at the position between the intersection of the first and second optical waveguides 21 and 22 and the other end of the third optical waveguide 23, that is, at the position into which the dielectric multilayer film filter 36 is to be inserted, across the optical waveguide substrate 31 at substantially a right angle thereto.
The first optical waveguide chip 40A that is one of the halves of the optical waveguide device 40 comprises: a half optical waveguide substrate 31 A; the first and second optical waveguides 21 and 22 of the optical waveguide 2 formed on the surface of the half optical waveguide substrate 31 A; a half clad layer 32A formed on the surface of the half optical waveguide substrate 31 A in such manner that these first and second optical waveguides 21 and 22 are covered with the half clad layer 32A; a dielectric multilayer film filter 41 formed by deposition of a dielectric multilayer film on an area of the end surface of the first optical waveguide chip 40A at the cut side thereof, the area including the intersection of the first and second optical waveguides 21 and 22 exposed on the end surface of the half clad layer 32A; and the light source 33 disposed to be opposed to the one end surface of the first optical waveguide 21. On the other hand, the second optical waveguide chip 40B that is the other of the halves of the optical waveguide device 40 comprises: a half optical waveguide substrate 31B; the third optical waveguide 23 of the optical waveguide 2 formed on the surface of the half optical waveguide substrate 31B; a half clad layer 32B formed on the surface of the half optical waveguide substrate 31 B in such manner that the third optical waveguide 23 is covered with the half clad layer 32B; and the photodetector 34 disposed to be opposed to the one end surface of the third optical waveguide 23.
The first optical waveguide chip 40A and the second optical waveguide chip 40B constructed respectively as described above are fixed to each other to obtain the optical waveguide device 40 after the intersection of the first and second optical waveguides 21 and 22 exposed on the end surface of the half clad layer 32A of the first chip 40A is opposed to the end surface of the third optical waveguide 23 exposed on the one end surface of the half clad layer 32B of the second chip 40B, and then, the mutual positioning between the intersection of the first and second optical waveguides 21 and 22 and the end surface of the third optical waveguide 23 is conducted such that the maximum quantity of light can be obtained.
The optical waveguide device 40 also operates as a WDM device like the optical waveguide device 30 shown in FIG. 1. For example, light L1 having its wavelength of 1.31 xcexcm emitted from the light source 33 propagates through the first optical waveguide 21, is reflected by the dielectric multilayer film filter 41, propagates through the second optical waveguide 22, and is emitted to the outside. On the other hand, light L2 having its wavelength of 1.55 xcexcm incident on the other end surface of the second optical waveguide 22 from the outside propagates through the second optical waveguide 22, passes through the dielectric multilayer film filter 41, propagates through the third optical waveguide 23, and is incident on the photodetector 34.
In such manner, in case of the prior optical waveguide device 40 shown in FIG. 2, the dielectric multilayer film filter 41 is formed directly on the area of the end surface of the half clad layer 32A including the intersection of the first and second optical waveguides 21 and 22. As a result, a loss of light is reduced, and the deterioration in the characteristic of the optical waveguide device can be fairly improved. In other words, the above-mentioned disadvantages resulting from the optical waveguide device 30 shown in FIG. 1 in which a slit is formed to insert a dielectric multilayer film filter thereinto and then the filter is fixed can be removed.
However, in the prior optical waveguide device 40 shown in FIG. 2, a process or procedure called active alignment in this technical field have to be used in case of aligning the first and second optical waveguides 21 and 22 with each other to obtain the maximum quantity of light and thereafter fixing them to each other.
In case of aligning the first and second optical waveguides 21 and 22 with each other and coupling them to each other by use of the active alignment process, the following process or procedure must be carried out, which comprises the steps of: inputting light from a light source not shown into the input end of the second optical waveguide 22 of the first optical waveguide chip 40A; inputting the light emitted from the output end of the second optical waveguide 22 through the dielectric multilayer film filter 41 into the input end of the third optical waveguide 23 of the second optical waveguide chip 40B; locating a position at which the maximum quantity of the light propagating through the third optical waveguide 23 can be obtained (usually, the second optical waveguide chip 40B is mounted on a X-Y-Z axis stage which is movable at high accuracy in the directions of three axes of X axis, Y axis and Z axis, and the position thereof is precisely adjusted to find a position at which the quantity of light received by the second optical waveguide chip 40B becomes maximum using an optical power meter connected to the output end of the third optical waveguide 23); and fixing both the optical waveguide chips 40A and 40B to each other.
The alignment process stated above is complicated and troublesome works, and further, the aforementioned X-Y-Z axis stage, the light source, the optical power meter, and the like have to be used. As a result, the manufacturing cost of the optical waveguide device comes to very high. In addition, in order to input light into the input end of the second optical waveguide 22 of the first optical waveguide chip 40A, it is necessary to couple between the light source not shown and the input end of the second optical waveguide 22 through an optical fiber, and in such case, the active alignment process must be also used. Likewise, in case of coupling between the output end of the third optical waveguide 23 of the second optical waveguide chip 40B and the power meter not shown through an optical fiber, the active alignment process must be used, too. Accordingly, there occurs a disadvantage that much time and prodigious labor are needed in order to align the two optical waveguide chips 40A and 40B with each other.
It is an object of the present invention to provide an optical waveguide device in which a plurality of PLC type optical waveguide chips are optically coupled with each other at high accuracy by a passive alignment process.
It is another object of the present invention to provide a method of manufacturing an optical waveguide device which comprises the steps of: cutting a PLC type optical waveguide device having an optical waveguide of a predetermined pattern formed on an optical waveguide substrate in a plurality of optical waveguide chips; providing a dielectric multilayer film filter on an exposed end surface of an optical waveguide of a predetermined one or more of the optical waveguide chips; and optically coupling two optical waveguide chips opposed to each other through the dielectric multilayer film filter therebetween by a passive alignment process.
In order to accomplish the foregoing objects, in one aspect of the present invention, there is provided a method of manufacturing an optical waveguide device comprising the steps of: forming an optical waveguide of a predetermined pattern on an optical waveguide substrate; forming at least one guide groove on the optical waveguide substrate in the longitudinal direction thereof; cutting the optical waveguide substrate having the optical waveguide and the guide groove formed thereon in the direction of traversing the optical waveguide substrate at substantially right angle thereto and passing through an intersection of the optical waveguide, thereby to form a plurality of optical waveguide chips; providing a dielectric multilayer film filter on an end surface of at least one of the optical waveguide chips, on which the intersection of the optical waveguide is exposing; fitting at least one guide pin in the guide groove of each of the plurality of optical waveguide chips in the state that the dielectric multilayer film filter is put between adjoining two optical waveguide chips, thereby to align the plurality of optical waveguide chips with one another; and bringing the aligned plurality of optical waveguide chips into contact with one another and fixing them.
In another aspect of the present invention, there is provided an optical waveguide device comprising: a plurality of optical waveguide chips formed by cutting an optical waveguide device comprising an optical waveguide substrate having an optical waveguide of a predetermined pattern formed thereon and at least one guide groove formed on the optical waveguide substrate in the longitudinal direction thereof, in the direction of traversing the optical waveguide substrate at substantially right angle thereto and passing through an intersection of the optical waveguide; a dielectric multilayer film filter provided on an end surface of at least one of the optical waveguide chips, on which the intersection of the optical waveguide is exposing; and fixing means fixing the plurality of optical waveguide chips aligned with one another by use of the guide groove in the state that they are in contact with one another through the dielectric multilayer film filter put between adjoining two optical waveguide chips.
In a preferred embodiment, the optical waveguide and the guide groove are formed using photolithography technique and etching technique. It is preferable that two guide grooves of generally xe2x80x9cVxe2x80x9d-shape in section are formed on both sides of the optical waveguide.
In addition, the guide groove of generally xe2x80x9cVxe2x80x9d-shape in section may be formed by forming a mask of a predetermined pattern made of quartz system material on the surface of a clad layer covering the optical waveguide therewith using photolithography technique and etching technique, and thereafter, applying an anisotropic etching using KOH liquid. Alternatively, the guide groove may be formed by dicing.
In another preferred embodiment, grooves for positioning optical fibers are formed on the surfaces of both end portions of the optical waveguide substrate in the longitudinal direction thereof, on which the optical waveguide is not formed, the grooves being formed on the surfaces of the both end portions in the longitudinal direction of the optical waveguide substrate in the state that they are aligned with exposed end surfaces of the optical waveguide respectively.
The dielectric multilayer film filter may be a filter that is formed by deposition of a dielectric multilayer film on an end surface of one of the optical waveguide chips, on which the intersection of the optical waveguide is exposing, or may be a dielectric multilayer filter of thin film that is fixed on an end surface of one of the optical waveguide chips, on which the intersection of the optical waveguide is exposing.
In accordance with the present invention, a plurality of separated optical waveguide chips can be aligned with and re-coupled to one another at high accuracy by passive alignment using at least one guide groove and guide pin. Consequently, a loss of light due to insertion of a dielectric multilayer film filter or filters becomes much small, and the characteristic of an optical waveguide device can be greatly improved. Moreover, since the passive alignment is used, it is unnecessary to use expensive apparatus and/or instruments, which results in reduction in manufacturing cost of an optical waveguide device. Furthermore, time and labor needed to manufacture an optical waveguide device can be remarkably reduced.